Safety device for dynamo-electric machines



No. 6I0,904. Patented Sept. 20, I898. E. M. HEWLETT.

SAFETY DEVICE FOR DYNAIO ELECTRIC MACHINES.

(Application filed Apr. 4. 1898,) (N0 ModeL) 2 Sheets-Sheet l.

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No. 6|0,904. Patented Sept. 20, I898.

E. M. HEWLETT.

SAFETY DEVICE FOR DYNAMO ELECTRIC MACHINES.

(Appliution filed Apr. 4, 1898.) Modem 1 2 Shqets$haot 2.

Edward M. Hewletb,

UNITED STATES PATENT OFFICE.

EDIVARD M. I-IEIVLETT, OF SCHENECTADY, NE\V YORK, ASSIGNOR TO THE GENERAL ELECTRIC COMPANY, OF NEW YORK.

SAFETY DEVICE FOR DYNAMO-ELECTRlC MACHINES.

SPECIFICATION forming part of Letters Patent No. 610,904, dated September 20, 1898-.

7 Application filed April 4, 1898. Serial No. 676,310. (No model.)

To all whoiit it may concern.-

Be it known that I, EDWARD M. HEWLETT, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Safety Devices for Dynamo-Electric Machines, (Case No. 62%,) of which the following is a specification.

10 In the operation of dynamos running in multiple, which is in modern practice the only method in use of employing a number of machines upon the same load, it becomes necessary to regulate the terminal voltage of the different generators to substantial equality, of course considering the character of the machines, the different circuit-resistances, the. Itis well known that if the speed of the dynamo is increased the terminal voltage rises. Under some circumstances, as when a large load is suddenly thrown off the station for instance, in a power-station when a number of stationary motors are shut down at noon or in the evening, or in a lighting-station when the lights in business-houses or dwellings are extinguished in large numbersthe engine or other prime mover may race, at least until its speed is controlled either by the regulator or by hand. In such a case the terminal voltage will rise with such rapidity that the machine may take practically all the load on the station,'and in some cases, such as that of a large direct-driven generator, may even for a time try to drive the other 3 5 machines as motors. The possible disastrous consequences are readily perceived. To a less degree a similar trouble might arise with a single dynamo if its prime mover should race. This may happen from the causes al- 40 ready pointed out. It is peculiarly liable to occur in operating electric railways, where it is impossible to prevent the simultaneous starting and stopping of many cars. In large systems this generally averages up, so that a fair constancy of load is attained; but in interurban work, where trains of greater weight use more current at starting, or on smaller roads, the fluctuations of load are more severe. Here the injurious effects upon the dynamo are rather mechanical than electrical,

arising from the high speed, though it is manifestly undesirable that tile machine should be operated at an excessive voltage, for which its insulation is insufficient.

To provide for the difficulties here briefly 5 indicated, I have devised an apparatus which combines the functions of a speed-governor and a circuit-interrupter in such a way that at a desired maximum speed it will not only open the electric circuit, preventing damage to the dynamo, but will also stop the supply of power to the prime mover, so that the speed is immediately and greatly reduced. By this arrangement danger of injury, electrical or mechanical, is very much reduced and practically eliminated. I have illustrated the illvention in the drawings annexed to this application as applied to a steam-engine in a form in which it has been practically used with success. It may be utilized with other prime movers, such as water-wheels, though in that particular case it is well to shut off the power gradually rather than suddenly for well-known reasons. The modifications necessary for attaining this end will be obvious to one skilled in the art. 7

In the drawings, Figure l is a side elevation of an embodiment of my device applied to the steam-chest of an engine. Fig. 2 is a diagram of circ1;1its,including a proper circuit-breaker. Fig. 3 is a diagrammatic illustration of a number of machines in a power-house employing my invention.

A is the steam-chest of an engine, and B is the main steam-pipe. 8 5

D is the usual throttle-valvet'or cutting off the supply of steam.

C is another valve, shown as a balanced flap-valve under the control of the governor I. It is connected to the governor by a bello crank C and a rod Ciattached to the bellcrank E. To the other arm of the bell-crank E is fastened the weight G, sliding upon the stud G and provided with a detent A rod F, with locknuts, furnishes a means of adjusting the throw of the weight G and the stroke of the crank E. The detent bears upon a latch H. The rod II is connected at one end to the latch, and at the other end is a slotted link 72, in which slides the pin 79 upon one arm of the bell-crank lever K, the other arm of which is attached to the rod I, controlled by the governor I. The set-screw h serves to adjust the point at which the pin will cause the device to act. A belt L connects the governor with the engine-shaft. (Not illustrated.) In operative relation with the valve is the switch M, consisting of the switch-blade m, connected by'a rod M with an'arm of the bell-crank lever E. A contact m is in the path of the switch-blade m.

In Fig. 2 the generator N is shown in diagram connected between the bus-bars. In the lead from the generator to the negative bus is the circuit-breaker O. The general type of this is fully described in the patent to W. B; Potter, No. 533,083, so that a minute description is unnecessary, particularly as it forms no part of the present invention, in op erating which some other type might be used.

' It is provided with main terminals p p and a ries coil Q.

bridging-terminal P,withdrawn by the spring P when the latch R is tripped by the armature R. The latter is controlled by the se- To these 'parts I add in my invention the shunt-coil Q, preferably, because most conveniently, acting upon the same armature. The circuit of this coil is controlled by the switch M and is connected, so that it also is opened by the circuit breaker when the latter blows, opening the circuit of the switch M.

In Fig. 3 I illustrate three generators N N N with their respective engines, all supplying common bus-bars. Each of these generators is provided with its own circuit-breaker O and an auxiliary switch M, the apparatus being simply a duplication of the construction shown in Figs. 1 and 2.

The operation of the parts is as follows: So long as the engine A is running below a certain maximum speed the governor rotates without affecting the switch M or the valve 0 but when the speed rises beyond the maximum desired the pin k strikes the adjustingscrew h in the end of the sloth, pulls the bar II, and trips the latch G The weight G then drops and closes the valve 0, shutting off steam from the engine. At the same time the switch-blade m is drawn across the contact m, closing the circuit of the shunt-coil Q and opening the circuit-breaker.

The particular construction of the circuitbreaker with more than one tripping-coil is susceptible of more than one useful application. In my pending application, Serial No.

650,759, filed September 7, 1897, I have shown and claimed, broadly, the construction here indicated.

WVhat I claim as new, and desire to secure by Letters Patent of the United States, is-

1. The combination with an electric generator, a prime mover driving the generator, a

governor for the prime mover, and means controlled by the governor for interrupting the circuit of the generator.

2. The combination with an electric generator, a steam-engine driving the generator, a governor for the engine, and means controlled by the governor for interrupting the circuit of the generator when the engine tends to race.

3. The combination with a dynamo and a prime mover, which drives said dynamo, of a mechanism electrically connected with said dynamo and mechanically connected with the governor of the prime mover, whereby upon an excessive speed being attained, the gov ernor acts to automatically stop the prime mover and cut the dynamo out of circuit.

4. In an electric generating-station, a number of dynamos in an electric circuit, in combination with one or more engines for driving them, one or more engine-governors, and a mechanism or mechanisms connected therewith and electrically connected with a source I of current, whereby, upon the engine racing, the governor will operate said mechanism to automatically cut off the power-supply, and cut out the dynamo or dynamos from the circuit.

5. The combination with a dynamo, and a circuit-breaker in circuit therewith, of an engine driving the dynamo, a mechanism electrically connected with the dynamo and controlling a valve forthe engine, a weight connected with the mechanism, and mechanism controlled by the governor of the engine normall y holding the weight; whereby, upon the engine attaining excessive speed, the governor will act to drop the weight and operate the mechanism connected therewith to stop the engine, operate the circuit-breaker and cut the dynamo out of circuit.

6. In an electric generating-station, generators electrically connected through a workcircuit, a circuit-breaker for each generator, branch circuits connecting a coil upon each circuit-breaker with a source of current, and a normally open switch in each branch cir cuit; in combination with an engine, a governor, a cut-off valve, and mechanism connecting the governor with the switch and the cut-off, whereby when the engine races, the cut-off and the circuit-breaker are simultaneously operated.

I11 witness whereof I have hereunto set my hand this 2d day of April, 1898.

EDWARD M. HEWLETT.

Witnesses:

B. B. HULL, M. H. EMERSON. 

